Oscillograph driving mechanism



Nov. 28, 1933. G. 1.. DIMMICZK OSCILLOGRABH DRIVING MECHANISM Filed Sept. 16, 1932 E r i INVENTOR 61.; DIMM CK BY ATTORNEY Patented Nov. 28, 1933 PATENT OFFICE v 1,936,833 v OSOILLOGRAPII DRIVING MECHANISM Glenn L. Dimmick, Westmont, N. 3., assignor to Radio Corporation of America, a corporation of Delaware Application September 16, 1932 Serial No. 6339147 '9 Claims. 7 (01. 171-95) This invention relates to galvanometers and particularly the variety thereof used in oscillographs such, forexample, as are used in recording sound upon film by the variable area method.

The invention relates more particularly to a novel manner of mounting the vibrating reed in order to avoid resonant vibration thereof within the range of operation of the apparatus, and to a novel manner of mounting and actuating the mirror in order to secure a large angular'defieetion thereof on relatively small deflection of the driving member, and to likewise render the mirror system substantially aperiodic. within the rangeof operation of the device. I

One object of the invention is to providea galvanometer having a reed which is capable of being tuned to frequencies outside of the recording device, thereby avoiding peaks in the response curve of the device.

Another object of the invention is to provide a mounting for the said reed which will maintain it definitely fixed in position after it has been adjusted.

- Another object of the invention is toprovide novel means for damping the vibrations of the reed in order to avoid bothresonant and harmonic vibration thereof.

Another object of the invention is to provide anovel connection between the reed and the mirror whereby the angular movement ofthe mirror is many times greater than that of the reed.

Another object of the invention is to provide a suspension for the mirror, the periodicity of which will not aflect the operation of the mirror.

Another object of the invention is to provide a novel damping means for the mirror.

Anothertobject of the invention is to provide a galvanometer which is both compact and rugged r of the device as follows: Upon the base member .1 are mounted two permanent magnets 2 and 3. These magnets carry a pair of silicon steel pole pieces 4 and 5 between which is supported a silicon steel reed 6. Two spacers .7 of non-magnetic material hold pole pieces! and 5 apart to form air gaps 8 at -vent vibration of the prongs.

'the fixed end or the reed firmly between the pole pieces.

Around the reed are placed tw'o coils 9 and 10, one of which serves to carry the acoustically modulated current from the-speech amplifier of a sound recording device, and the other of which serves to carry the bias current from what is. known as an anti-ground noiseqamplifler and whichshifts thezero of the galvanometer in proportion to the amplitude of the impulse transmitted to the other coil, in a manner analogous to that of RobinsonPatent No. 1,854,159, April 12, 1932.

A mirror 11 is carried upon the metallic suspension strip 12, to which it is firmly attached I0 and to the rear of the mirror is attached a small plate 13 which has a curve in its rear face fitted over a knife-edge on the end of the reed 6. The knife-edge thereby serves as a pivot about whichthe mirror 11 can be rotated in response to J6 oscillation of the reed.

The member 12 is preferably a .phosphor bronze ribbon and the two ends thereof are metened to prongs 14 and 15 which extend downwardly' from the curved member 16 for a'purpose which will be later described. The bronze strip passes between the mirror 11 and the plate 13 so that its plane is a slight distance away from that of the knife-edge upon the end 01' the reed 6. The prongs 14 and 15 press rather tightly 85. against the pole pieces 5 and 4 in order to pre- In adjusting the device the screw 17 is tightened, thereby flegdng the curved member 16 and rotating the prongs 14 and 15' in opposite directions until an appropriate tension is placed upon the phosphorbronre ribbon 12.

An adjustable magnetic shunt 19 is provided for the purpose of adjusting the reed 6 to the exact magnetic center between the pole pieces.

A damping member 20 in the form of a disc or slab oi rubber maybe providedfor the purpose of damping the vibrations of the reed 6.

The operation of the device is as follows: The magneta'zend 3 are arranged so that their similar poles are adjacent and therefore the polarity of the pole pieces 4 and 5 corresponds with thatot the magnets. Thereed 6 since it is supported at 7 between the pole places is magnetically neutral and'any deviation from neutrality, which would .106 tend to cause it to lie to one side or the other of on exactly central position between the-pole pieces 4 and 5 is corrected by adjusting the magnetic shunt 19. each'aideotthe reedeendlikewieeeervetoclamp This adjustment isaocompllshed by removing will not cause a change in the adjustment and the screw 21 is then replaced.

When a current flows through either of the coils 9 or 10 it produces a change in the polarity of the outer end of the reed 6 and causes a corresponding shift in its position toward one pole piece or the other. This shifts the position of the knife edge at the back of the plate 13 and, due to the manner in which the plate is suspended,'causes a corresponding rotation of the plate 13 and the mirror 11 about an axis which is perpendicular to the plane of the paper in Fig. 1. It will be apparent that this axis will fall within the plate 13 and can be' located at the center of the triangle defined by the knife edge and the two points of intersection of the supporting strip 12 with the plate 13. Any movement of the reed is therefore reproduced as a correspondingly magnified movement of the mirror 11.

This large magnification of the movement and the small mass and, therefore, small inertia of the movement parts permits the reed 6 to be made relatively stiff so that the natural period of the system is extremely high, thereby avoiding resonance peaks and at the same time permits the use of relatively great damping in the member 20 so that a very accurate proportionality exists between the audio frequency input currents and the deflections of the mirror over the entire range of audio frequencies.

The great stifiness permissible. in this system and likewise the large magnification of the movement permit the use of a mirror of much greater size than has been heretofore possible since the effect of the mass of the mirror becomes relatively small. The use of a larger mirror permits the transmission of a much greater quantity of light to the film in sound recording and thereby materially increases the over-all efficiency of the apparatus.

It will be apparent that the use of my construction is not limited to a reflecting galvanometer for sound recorder but that the mirror and mirror support may be omitted and any other equivalent-mechanism substituted therefor such, for example, as a diaphragm or the like so that the device can be used with either a microphone or loudspeaker or it may be used in any other desired manner, however, I have so far found the greatest utility for this construction in connection with the reflecting galvanometer forsound recording and I have accordingly illustrated the preferred form of my invention.

I claim:

1. A galvanometer comprising a movable reed having a knife edge at one end thereof, a vibration reproducing member in cooperative relation to said knife edge, and a flexible supporting means extending in the direction of vibration of said reed and retaining said member thereagainst. I

2. A galvanometer comprising a movablereed having a knife edge at one end thereof, a vibration reproducing member incooperative relation to said knife edge, and a flexible supporting means extending in the direction of vibration of said reed and retaining said member thereagainst, the said flexible supporting means being maintained under tension.

3. An electric motor of the oscillograph type comprising a pair of pole pieces, a vibratable reed supported therebetween, means maintaining said reed mechanically equi-distant between one portion of said pole pieces and means for adjusting the magnetic relation of said parts whereby the said reed is maintained equi-distant between another portion of said pole pieces.

4. An electric motor of the oscillograph type comprising a pair of pole pieces, a vibratable reed supported therebetween, means maintaining said reed mechanically equi-distant between one portion of said pole pieces and a magnetic shunt in cooperative relation with the fixed end of said reed for adjusting it to the magnetic center between the said pole pieces.

5. Means for supporting a galvanometer suspension under tension comprising a supporting plate, a curved member in cooperative relation with said supporting plate, a pair of arms integral with said curved member and extending in a direction perpendicular to the surface of said supporting plate for supporting the said suspension, and means for adjusting the curvature of said curved member in relation to the supporting plate whereby the distance between said arms is adjusted 6. An electric motor of the oscillograph type comprising abase member, a support extending therefrom, a pair of pole pieces secured to said support and a pair of magnets supported in cooperative relation with the outer ends of said pole pieces and on opposite faces thereof.

It A galvanometer comprising a movable reed having a knife edge at one end thereof, a vibration reproducing member in cooperative relation to said knife edge, and a flexible supporting means for retaining said member thereagainst.

8. The combination of a movable reed having a knife edge at one end thereof, a vibration reproducing member in cooperative relation to said knife edge, and a flexible supporting means for said member extending across said edge.

9.. A galvanometer comprising a movable reed having a knife edge at one end thereof, amirror in cooperative relation to said knife edge, and a flexible supporting means extending in the direction of vibration of said reed and retaining said mirror thereagainst.

GLENN L. DIMMICK. 

